The optical detection of hydrocarbon fires is often rendered difficult by the presence of background radiation, such as from the sun, from artificial light, or from a hot metallic body. Although detectors are known which can discriminate between fire radiation and solar radiation, so that the detector will not provide an alarm in response to solar radiation, such a detector is "blinded" by the solar radiation and will not respond to fire radiation while exposed to solar radiation.
It is known that hydrocarbon fires produce radiation with peaks at various wavelengths. Efforts have been made to utilize these peaks for detection of such fires; however, such detectors are susceptible to false alarms from solar or black body radiation, either of which may produce radiation of substantial intensity in the particular wavelengths to which the detector is responsive.